The present invention relates to an apparatus and method for washing an electrode plate core for an alkaline battery and a method for manufacturing an alkaline battery that has undergone such a washing method.
As known in the art, alkaline batteries, such as a nickel-cadmium battery and a nickel-metal hydride battery, are widely used as power supplies for portable information terminals, vehicles, or the like. The positive electrode in each of the above alkaline batteries includes a conductive core and an active material, which is carried by the core. The core may be a foam nickel substrate or a porous metal substrate, which is formed from a sintered alloy.
When manufacturing the porous metal substrate, which is used to form the electrode plate core, metals other than nickel and iron (e.g., copper) may mix in the electrode plate core as impurities. If the amount of the mixed metal impurities is large, such metal impurities may dissolve from the core into an electrolytic solution and deposit in the solution. This may cause fine short-circuiting between the positive and negative electrode.
Accordingly, in the prior art, Japanese Laid-Open Patent Publication No. 2004-71534 describes a technique for washing off metal impurities when manufacturing the electrode plate core. In this publication, the washing of the electrode plate core is performed as described below.
The porous metal substrate used as the electrode plate core is wound in a coil-shaped manner as a hoop. In the above publication, as shown in FIG. 1, a hoop 50 of a porous metal substrate is immersed into an aqueous solution 51 containing ammonium ions and hydrogen peroxide to wash off copper, which is a metal impurity.
In this manner, in the prior art, a great amount of an electrode plate core can be washed in hoops. However, in a hoop that is wound in a coil-shaped manner, the bonding rate at the central portion of the hoop is high. Thus, it becomes difficult for the washing solution to enter and sufficiently wash the central portion. As a result, the hoop must be immersed in the solution for a long period of time so that the solution can enter the central portion of the porous metal substrate and wash off the metal impurities.
Most of the hydrogen peroxide in the solution decomposes when the temperature of the solution rises to about 35° C. Thus, the temperature of the solution must be accurately controlled during the washing. However, in the above-described technique of the prior art, exothermic heat generated by chemical reactions is large since a great amount of the electrode plate is washed in hoops with the solution. As a result, the controlling of the temperature is difficult.